The present invention relates to a rocker arm made of sheet metal used for a valve gear of an automobile engine, and a method of manufacturing the rocker arm.
A rocker arm made of sheet metal provided in a valve gear of an automobile engine is formed in such a manner that a roller is arranged between a pair of opposed side walls provided in a body made of sheet metal and this roller is pivotally supported by a spindle via needle rollers. Connecting walls are formed so as to respectively connect the opposed side walls to each other and are arranged in the longitudinal direction. One of the connecting walls is used as a lash adjuster receiver and the other connecting wall is used as a valve stem receiver.
In this rocker arm made of sheet metal, when a cam is contacted with the roller and rolled on it and the body is oscillated round the lash adjuster which functions as a fulcrum, and the valve stem is moved upward and downward by the valve stem receiver, the valve can be opened and closed. Concerning this structure, for example, refer to Patent Document 1.
Patent Document 1: JP-A-6-74004
A lubricating state on the sliding contact face of the valve stem receiver of the rocker arm made of sheet metal, on which the valve stem slides and contacts, is not so good, so that abnormal abrasion and pitching tend to occur on the sliding contact face. As a countermeasure for preventing the occurrence of the abnormal abrasion and pitching, generally, a crowning is formed on the sliding contact face of the valve stem receiver or surface pressure of the contact with the valve stem is reduced.
However, when the viscosity of engine oil used as lubricant is decreased, the lubricating state of the sliding contact face of the valve stem becomes more severe, and the above countermeasure for preventing the occurrence of abnormal abrasion and pitching is not sufficient.